surveying Engineering Fly Levelling Fly leveling: -Fly leveling is just like differential leveling carried out to check the accuracy of leveling work. It is a very approximate form of leveling in which sights are taken as large as possible. in this method, a line of levels is run to determine approximately reduced levels of the points carried out with more rapidly and less precision The aim of fly Levelling: The main purpose of this type of leveling is to check the values of the reduced levels of the bench marks already fixed. In this method only back sight and foresight are taken. There is no need of intermediate sights. However great care has to be taken for selecting the change points (Turning Points) and for taking reading on the change points because the accuracy of leveling depends upon these -Create Bench Marks (BM). Bench Marks Bench Mark is a point of known elevation, there are three Type of Bench Marks 1-Perment Bench Mark. 2-Orbitrary Bench Mark . 3-Temporary Bench Mark . -Leveling Process Calculation. 1. Height of collimation method 2. Rise and Fall method How do we find horizontal distance using levelling Machine. Fly Levelling Close loop survey. Fly and Differential leveling Using (Rise & fall) and (HI)methods. *Checks for Errors -Misclosure Allowable closing error Where: D =Distance in km E = Misclosure error in (mm). C = 30 for fixed levelling process in rough ground. C = 15 for normal leveling in flat area (Good work) Fly Levelling example Computation of Elevations for an open loop survey H.I method Computation of Elevations Differential Leveling Computation of Elevations -Correction For Errors in Leveling 1. Errors Due to the line of sight being not horizontal 2. Error Due to Curvature and refraction. Errors in differential leveling: - 1) Non adjustment of the instrument: - a) Adjustment of cross-wire ring b) Adjustment of the bubble tube c) Adjustment of line of sight 2-Errors in levelling • Collimation line • Parallax • Change point instability • Instrument instability • Benchmark instability • Staff reading errors , • Staff verticality • Level Instrument shading • Temperature on staff • Booking errors) • Earth curvature • Refraction • The Bubble not center. 3-Constant error (instrumental error): A. Non vertically of the staff. B. Collimation error in the instrument. C. Staff gradation error. 4- Random error (natural error): A. Effect of wind and temperature. B. Soft and hard ground. C. Change points. CP D. Human deficiencies and neglect Prepared by: Asst. Prof. Salar K.Hussein Mr. Kamal Y.Abdullah Asst.Lecturer. Dilveen H. Omar Erbil Polytechnic University Technical Engineering College Civil Engineering Department

1. Fly Levelling
surveying Engineering
2022- 2021
1
Erbil polytechnic university
technical engineering college
civil engineering department
Prepared by
Asst. Prof. Salar Khudhur Hussein
Ass. Lecturer Mr. Kamal Yaseen
Ass. Lecturer Ms. Dilveen H. Omar
Benchmark

2. Fly Levelling
. Fly leveling: -Fly leveling is just like differential leveling carried
out to check the accuracy of leveling work. It is a very approximate
form of leveling in which sights are taken as large as possible. in this
method, a line of levels is run to determine approximately reduced
levels of the points carried out with more rapidly and less precision
The aim of fly Levelling: The main purpose of this type of leveling is
to check the values of the reduced levels of the bench marks already
fixed. In this method only back sight and foresight are taken. There is
no need of intermediate sights. However great care has to be taken for
selecting the change points (Turning Points) and for taking reading on
the change points because the accuracy of leveling depends upon
these. 2

3. Create Bench Marks (BM)
3

4. Bench Marks
Bench Mark is a point of known elevation, there are three Type of Bench Marks
1-Perment Bench Mark.
2-Orbitrary Bench Mark .
3-Temporary Bench Mark .
1-Permanent bench marks
• These benchmarks are written on permanent objects such as milestones, culverts,
bridges etc. their values are clearly written and their position are recorded for
future reference.
4
City Center BM
Shanadr BM

5. Introduction to Surveying (BPD)
LEVELLING PROCEDURES
Department of Structural Engineering Technology
College Of Technology
5

6. 6

7. Bench Mark B. M
RLBM
Benchmark
Datum
7
2.Datum Surface; Datum surface is
any level surface to which the elevations
of all points may be referred. The mean
sea level(MSL) is usually adopted as
datum.
Mean Sea Level

8. Leveling Process Calculation
To find reduced level of points, there are two methods:
1. Height of collimation method
The following formula will serve as a guide to the reduction of level by this method;
H. I= B. S + R. L.BM
R. L (new)= H. I – staff reading(I.S or F.S)
H. I. (old) – F. S = R. L (new) at change point
R. L. (new) + B.S = H. I. (new)
2. Rise and Fall method
Rise or fall = B.S – F.S or I.S
= I.S preceding point – I.S following point = I.S – F.S
R.L of any point = R.L B.M + {Rise (+) or fall (-)}
Distance (AB) = (Upper – Lower)x 100
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H.I
R.L
A B
Sea level-Datum
Elevation

9. How do we find horizontal distance using
levelling Machine
9

10. 10
BM=100
ST1
ST2 ST3
ST4
ST5
TP1
TP2
TP3
TP4
TBM=?
Fly Levelling
Close loop survey

11. Fly and Differential leveling Using (Rise&fall)
and (HI)methods
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12. Checks for Errors
1. Closed loop check To close the loop the survey is continued back to the
beginning. Any difference in elevation for BM1 between the initial elevation of
BM1 and the closing elevation of BM1 is error.
2. The Note check (The Computation check) The note check uses an equation:
∑B.S - ∑F.S = R.L last - R. L first
3. Allowable error (Misclosure); Is the difference between the known
benchmark and computed benchmark
misclosure =Known point- measured point =0
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13. Misclosure
•The amount by which the measured height
difference (DH measure) differs from the known
height difference derived from the RLs of the
starting and finishing benchmarks (DH known
Misclosure = DH known – DH measure
13

14. • The third check for error is also called the allowable error.
• It is common practice for the individual contracting the work to specify the acceptable level of
error. Professional standards may also specify allowable error.
The allowable error is based on an equation:
Allowable misclosure=E =C 𝑹
Where: C=constant C=12 for Mountain area C=30 for Ground levelling
R= is total distance by Km
Correction= E/n n=Number of T.P stations
Note:
• If actual misclosure<allowable misclosure(E), therefore the survey is acceptable. Unless, you
divide the error into turning points only.
• ΣBS - ΣFS only checks CALCULATION not OBSERVATIONS
• Observations checked by closing onto known final point MISCLOSURE
• Intermediate sights NOT checked by either.
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15. Table and Corrections,,, Misclosure = DH known – DH measure
point BS IS FS HI RL Corrections Corrected ,,RL DH Distance
15

16. Allowable closing error
Where:
D =Distance in km
E = Misclosure error in (mm).
C = 30 for fixed levelling process in rough ground.
C = 15 for normal leveling in flat area (Good work)
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17. Fly Levelling example
Computation of Elevations for an open loop survey
H.I method
Elevation 100.00
BS
12.64
Point
BM1
Elevation
BS HI FS
BM1
12.64 112.64 100.00
1. BS + Elevation = HI
BM2=124.47m
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18. Computation of Elevations
Elevation 100.00
BS
12.64
FS
3.11
Point
BM1
TP1
Elevation
BS HI FS
TP1
BM1
12.64 112.64
3.11 109.53
BS
10.88
10.88 120.41
100.00
18

19. Computation of Elevations
Elevation 100.00
BS
12.64
FS
3.11
Point
BM1
TP1
Elevation
BS HI FS
TP1
BM1
12.64 112.64
3.11 109.53
BS
10.88
10.88 120.41
FS
2.56
TP2
2.56
TP2 117.85
100.00
19

20. Computation of Elevations
Elevation 100.00
BS
12.64
FS
3.11
Point
BM1
TP1
Elevation
BS HI FS
TP1
BM1
12.64 112.64
3.11 109.53
BS
10.88
10.88 120.41
FS
2.56
TP2
2.56
TP2 117.85
BS
9.72
9.72 127.57
100.00
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21. Computation of Elevations
Elevation 100.00
BS
12.64
FS
3.11
Point
BM1
TP1
Elevation
BS HI FS
TP1
BM1
12.64 112.64
3.11 109.53
BS
10.88
10.88 120.41
FS
2.56
TP2
2.56
TP2 117.85
BS
9.72
9.72 127.57
BM2
FS
3.10
BM2 3.10 124.47
100.00
21

22. Differential Leveling
Computation of Elevations
Elevation 100.00
BS
12.64
FS
3.11
Point
BM1
TP1
Elevation
BS HI FS
TP1
BM1
12.64 112.64
3.11 109.53
BS
10.88
10.88 120.41
FS
2.56
TP2
2.56
TP2 117.85
BS
9.72
9.72 127.57
BM2
FS
3.10
BM2 3.10 124.47
100.00
22

23. Differential Leveling
Computation of Elevations
3. Change in elevation- summation of the backsight and
the foresight then subtract
+33.24 -8.77
Change in elevation = 33.24 -8.77 =24.47
Point
BM1
TP1
Elevation
BS HI FS
12.64 112.64
3.11 109.53
10.88 120.41
2.56
TP2 117.85
9.72 127.57
BM2 3.10 124.47
100.00
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Summation
Last RL – First RL =124.47 – 100.00 = 24.47 m
For check

24. Correction For Errors in Leveling
1. Errors Due to the line of sight being not horizontal
2. Error Due to Curvature and refraction.
Correct
reading
Actual
reading
Size of error depends on
sight length
24

25. Errors in differential leveling: -
1) Non adjustment of the instrument: -
a) Adjustment of cross-wire ring
b) Adjustment of the bubble tube
c) Adjustment of line of sight
2-Errors in levelling
• Collimation line
• Parallax
• Change point instability
• Instrument instability
• Benchmark instability

26. • Staff reading errors ,
• Staff verticality
• Level Instrument shading
• Temperature on staff
• Booking errors)
• Earth curvature
• Refraction
• The Bubble not centered
26

27. 3-Constant error (instrumental error):
A. Non vertically of the staff.
B. Collimation error in the instrument.
C. Staff gradation error.
4- Random error (natural error):
A. Effect of wind and temperature.
B. Soft and hard ground.
C. Change points. CP
D. Human deficiencies and neglect .
27